Seasonal soil water variation and root patterns between two semi-arid shrubs co-existing with Pearl millet in Senegal, West Africa

Soil water is an important resource that imposes limitations on optimal plant performance in semi-arid regions. In some of these regions, shrubs form a characteristic component of farmers’ fields and potentially impact crop productivity. Consequently, a 2-year study on soil water dynamics and shrub rooting patterns was conducted during the dry season and transition into the wet season with fields having Pearl millet intercropped with shrubs. Millet roots predominantly exploited the 0.2–0.5 m depth range with 95% of shrub roots in the upper 0.5 m. Soil volumetric water content (soil water content) decreased with greater radial distance from shrubs up to 2 m but progressively increased with soil depth. During the dry season, soil surrounding shrub roots was consistently moister than adjacent bare soil albeit at depth, soil moisture content declined steadly in the 0.9–1.2 m depth range due to depletion by shrub roots. On the contrary, the 0.2 and 0.4 m zones depicted slight increments in soil moisture which could be attributed to soil water redistribution by shrub roots. During the rainy season, shrub presence had a considerable impact on the fate of the field soil moisture regime with shrub roots serving as pathways for deep profile recharge. Shrubs exploited the deeper profile (0.9–1.2 m) as opposed to the Pearl millet (0.2–0.5 m) suggesting that intercropping of annual crops with shrub stands could serve as an innovative and viable agronomic option in these vulnerable Sahel agro-ecosystmes.